


9 out of 10 Dentists Recommend

by showmeurteef



Category: Monsta X (Band)
Genre: Begging, Degradation, Light Dom/sub, Masturbation, Other, Praise Kink, Spanking, Toothbrushing, ao3 user showmeurteef writes teef centric sex, brat!changkyun, genderfuck!changkyun, kihyun's tongue gets to be the star for once, light gagging, light pain kink, she/her baby boy, spit, spit kink??
Language: English
Status: Completed
Published: 2020-02-29
Updated: 2020-02-29
Packaged: 2021-02-28 01:35:41
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,234
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22535590
Author URL: https://archiveofourown.org/users/showmeurteef/pseuds/showmeurteef
Summary: “If you don’t brush your teeth right now, I’m not kissing you good night.”Changkyun’s toes practically leave skid marks on the floor as she grinds to a halt.kihyun helps changkyun put a little more effort into her dental hygieneextended/explained warnings within
Relationships: Im Changkyun | I.M/Yoo Kihyun
Comments: 10
Kudos: 68





	9 out of 10 Dentists Recommend

**Author's Note:**

> warnings:  
> -established relationship = established boundaries etc  
> -pls be careful w puttin objects in ur mouth like this cuz choking hazards etc,,, pls practice safe careful well thought out sex

Changkyun pads out of the little bathroom, squeezed into an Invader Zim pajama set that’s _basically_ her size, air conditioning nipping at her freshly washed cheeks, and used towel forgotten around her neck. Her tired brain drowns in thoughts of the pillows and _sleep_ that await her just across the hall. But Kihyun’s furrowed eyebrows and hardened lip block her path to their bedroom.

“No _way_ was that a full two minutes,” he huffs with a scowl that might as well be a cinderblock wall.

“Two minutes?” Changkyun tries to sidestep him —even going so far as to fake him out before dipping in the opposite direction— but Kihyun catches her shoulders. “Two minutes of what?”

 _“Teeth brushing,”_ Kihyun sighs, as if a grown joyfriend nagging his own grown joyfriend about dental hygiene is the most standard joyfriend behavior in the world.

“Dude. Chill.” Changkyun crosses her arms over Gir’s face, wrinkling the already worn fabric. “I’m not gonna get a cavity overnight. I even flossed, bro.”

“The National Dentists’ Association recommends at _least_ two minutes of brushing, twice per day, _bro."_ Kihyun’s hand splays over Gir’s wrinkled eyes and _shoves_ Changkyun back into the bathroom.

Changkyun purses her lips and huffs. She knows better than to argue with Kihyun about personal hygiene, but she’s _really_ tired and she’s _just_ gotten ready for bed and she’s been thinking about snuggling under their fluffy comforter _all day._

So, she argues.

“What are you, the goddamned tooth fairy? Gonna take back the nickel from under my pillow if I don’t brush my teeth for two minutes like a good little boy?” Changkyun clasps her hands together in mock fear, gasping and wiggling under Kihyun’s hard, _harder_ gaze. She remembers the damp towel, and bestows it upon Kihyun’s stiff shoulders with a pat on the cheek— like a medal ceremony, but snotty. “I’ll brush for _three whole minutes_ in the morning. Promise.”

She slinks as far as the bedroom threshold before an exasperated sigh puffs out of Kihyun’s heartless chest.

“If you don’t brush your teeth _right now,_ I’m not kissing you good night.”

Changkyun’s toes practically leave skid marks on the floor as she grinds to a halt.

“No good morning kiss either?”

“No.”

“Bro—”

_“No.”_

Changkyun turns to find Kihyun neatly preparing her toothbrush. Running it under the faucet for exactly two seconds. Tapping it gingerly against the sink. Squeezing a precisely pea-sized dollop of toothpaste onto it. All with a face cast in cold, unforgiving iron.

Changkyun glares between him and the picture-perfect toothbrush. This isn’t about dental hygiene anymore; this is a matter of _pride_.

So, she stamps her foot, crosses her arms even tighter, and lets out a frustrated whine.

“Why does it even _matter?_ It’s not like you can _catch_ cavities.” Kihyun just extends the toothbrush towards her, as firm as ever. “If you care so much, why don’t _you_ do it?”

“Is _that_ what it’s gonna take? You’re really gonna be _such_ a big baby that _I’m_ gonna have to brush your teeth for you?”

Changkyun matches Kihyun’s raised brow. Smooths out Gir’s face. Says nothing.

“You know what? _Fine,”_ Kihyun snaps. He perches on the lidded toilet and sharply gestures to his lap. “Sit.”

“Wait, what—”

“ _Sit_.”

Changkyun —sleepy brain still not quite processing that Kihyun is _actually_ willing to brush her teeth— straddles Kihyun in a daze. Kihyun’s jaw clenches at being smushed between cold porcelain and Changkyun, but levels his sharp gaze with Changkyun’s confused blinking.

“Are you _really_ gonna—”

Kihyun grabs her chin, fingers digging into her cheeks to keep her mouth open, and glares at her wet, wriggling tongue.

“No talking.”

Changkyun isn’t positive, but she thinks Kihyun might be using his bedroom voice? Or, maybe, stern, naggy Kihyun always sounds a little sexy , and Changkyun has never paid close enough attention to tell? Regardless, her dick kind of tingles when Kihyun snaps at her, when her shorts bunch up as she scoots forward, when the insides of her cheeks are pressed into her molars.

Confused horniness rises thickly from her throat. Kihyun’s eyebrows shoot straight up to his hairline, still damp from his earlier (painfully meticulous) bedtime routine.

“Are you...?”

Changkyun nods lightly in his grasp. Kihyun’s face molds like clay between irritation and surprise and something very, _very_ evil. He holds the toothbrush over Changkyun’s tongue.

“Good little boys don’t speak while their teeth get brushed all nice and clean. Maybe if you’re _real_ good the tooth fairy will give you something better than a nickel. Just say the word if it gets to be too much, hm?” Kihyun’s chin crinkles as he smiles, face _glowing_ with amusement at Changkyun’s expense. Changkyun, however, doesn’t think being held from sleep by a dirty talking tooth fairy roleplayer/dentistry enthusiast/persnickety asshole is very funny. At all.

So, she holds back her laughter and _bites_ the tooth brush. Her tongue worms its way around the prickly brush, licking every last bit of toothpaste from it as Kihyun’s displeased scowl returns.

Kihyun tries to tug the toothbrush out of her mouth, but Changkyun _grips_ the handle between her front teeth. Her tongue is coated in gloopy, gross spearmint and she’s a little concerned that playing tug of war with a hard plastic toothbrush might not be the _best_ thing for her teeth, but she _can’t_ lose this round. She already sat down on command and revealed her apparent horniness for tooth fairy roleplayer/dentistry enthusiast/persnickety asshole Kihyun, so she can’t _possibly_ let go—

Kihyun clicks his tongue.

Changkyun lets go.

Kihyun reaches for the toothpaste on the sink beside them with a wry smile. Changkyun begins to pout, to protest, to scrape up _some_ sort of defense, but Kihyun shakes his head.

“Mouth open.”

Changkyun’s mouth opens. She puffs hot, minty air in Kihyun’s smug face. She sinks more solidly into Kihyun’s thighs. She glares daggers at the new glob of toothpaste perched on the toothbrush.

“Big brat.” Kihyun tugs her face closer, fingers _digging_ into her jaw. “Let me take care of you.”

“This is so _pointless,_ though. Maybe if you weren’t such a finicky old bastard—”

“That’s funny; I seem to recall telling you not to speak mere _moments_ ago...” Kihyun hums. 

Changkyun rolls her eyes, but doesn’t say a word. Kihyun smiles at that, tilting Changkyun’s chin downward just a bit more harshly than necessary, and flattens the toothbrush against a couple of molars. The bristles part gently, making way for jagged little teeth. Kihyun brushes her molars gingerly— Changkyun might call his careful attention to every nook and cranny _sweet,_ if it weren’t for the bruising grip on her chin, or that evil grin, growing and growing as he moves the brush forward.

The plastic bits of the brush jab at her gums and the underside of her tongue. Stinging, ticklish, open. Her spit is thick with spearmint. The bristles whisper over her incisors.

Kihyun’s hand moves to cradle the back of her head. His eyes soften and his brow furrows as he focuses. He makes thoughtful little noises as he finishes Changkyun’s bottom teeth.

And Changkyun’s dick is kind of, perhaps, maybe just slightly, hard. A little too thick in her tiny Gir shorts. A little too heavy pressed against Kihyun’s tummy. 

“Now, close.” 

Kihyun taps the brush on her front teeth with another amused grin; a sprig of smugness that makes Changkyun want to bite the brush again. 

But, okay. Fine. Sure. Her brain’s gone a little gloopier than the toothpaste and her nerves prickle like the bristles over her gums. And what she wants most of all is for Kihyun to keep holding onto her, taking care of her; equal parts firm and tender.

So, she snaps her mouth shut, swallows thickly, and bares her teeth for Kihyun. Like a good little boy.

Kihyun strokes the back of her head, small fingers dancing to the shell of her ear, and laughs lightly when Changkyun’s eyes flutter shut. He gets a little less amused, a little more aroused when Changkyun starts to sag into his touch. Kihyun rubs her earlobe between his fingers, and Changkyun can _feel_ herself shrinking, melting in Kihyun’s eyes and fingers and lap. Teeth still bared. Wholly absorbed by the warm, zinging pressure of Kihyun’s fingertips.

And, for the life of her, she can’t remember why she was so resistant to this pampering in the first place. She likes being taken care of. Likes it _a_ _lot_. 

_“Finally.”_ Kihyun’s breath hitches as Changkyun squeezes his hips between her thighs, drawing impossibly closer. Heavier. _Needier._ “Can you let me finish brushing your teeth now? So we can go to bed?”

Changkyun nods. Her eyes slip shut. She clutches loosely at Kihyun’s shirt.

Kihyun tugs her bottom lip down, pinching and stretching to expose her bottom teeth to the bathroom’s crisp air, all the way down to their roots. The brush circles her teeth tightly, neatly. Catching in the little grooves between each tooth. Spreading foamy spearmint everywhere. Changkyun’s head moves on its own, gently mimicking the toothbrush’s circles.

Kihyun lets her bottom lip snap back up, and Changkyun’s knees knock against the back of the toilet. She opens her eyes to find Kihyun more focused than ever; Changkyun wants to say he’s made of cold porcelain just like the toilet, but she’s being good right now. She’s careful to puff her laughter out through her nose as Kihyun tilts her chin upward. 

The brush finds it's way to the back of Changkyun’s mouth, coming dangerously close to the squishy, wet entrance to her throat, before setting to work on her top teeth, scrubbing and swirling over molars. Bubbly toothpaste clings to each tooth. Threads of spit drip down from the roof of her mouth and land on her tongue, cool and minty. Kihyun blinks steadily at Changkyun’s squirming tongue.

An iron fist of need clenches Changkyun’s insides. She squirms. The careful brushing, the sticky wetness, the intimacy of having her mouth wide open for Kihyun make her _desperate_. She rubs her clothed dick against Kihyun’s tummy— _super_ subtly, though. Gently, even. She rubs it _so_ lightly, in fact, that Kihyun probably didn’t feel a thing.

So, Changkyun _grinds_ down into him with a heavy whine.

Kihyun presses the toothbrush to her tongue, flattening it out. The plasticky taste and forced stillness make Changkyun feel even _more_ urgent. Spit pools around her weighted tongue.

“Close your mouth.”

Changkyun quickly closes her lips around the toothbrush, biting the handle to keep it in place. Kihyun lets her hold it there, his own tongue swiping at his bottom lip, and places his hands on Changkyun’s hips. His thumbs expose bits of skin between her shirt and shorts as they trace whispery soft circles over her hip bones. Kihyun watches Changkyun’s face carefully, quietly; seeking out every infinitesimal reaction. Changkyun’s jaw tightens.

One of Kihyun’s hands slips into her shorts and pulls her dick out. Changkyun glances down. Finds her dick flushed and wet, base caught in the ring of Kihyun’s thick fingers, waistband biting into its soft skin. She whimpers, but keeps her hold on the toothbrush. 

Her mouth overflows with diluted mint and gloopy spit. The toothbrush is hard against her tongue, bristles tickling at her palette. She’d want to suck, if it weren’t so gross and uncomfortable. She swallows thickly.

Kihyun’s hold on her hip turns _bruising_ and Changkyun jumps. Kihyun starts jerking her off, dry fingers dragging heavily over her length; not picking up enough precome to do any good, not making enough friction to at least make the burn worth it. And he’s _grinning_ again. Because he knows it's uncomfortable. Because he knows it isn’t enough.

Changkyun bares her teeth and hisses around the toothbrush, “If you’re gonna take care of me, do it _right,_ you ass.”

“You think you know better than me? _You?_ ” Kihyun laughs sharply and continues to stroke her— _too fucking slowly._ “The useless baby who couldn’t even brush her teeth right?”

Changkyun pictures herself chomping right through the toothbrush and spitting the halves in Kihyun’s lap, freeing up her mouth to _properly_ argue. Kihyun’s eyes glint dangerously, like he knows exactly what Changkyun’s thinking. It sends a shiver down Changkyun’s spine. It makes her think disobedient thoughts even harder.

“That’s cute— _adorable,_ really. My baby thinks she’s so smart,” he coos, digs his blunt nails into Changkyun’s hip, and has the _audacity_ to let go of her dick. “My baby thinks she’s big and smart and tough enough to get away with being a brat— a brat to _me."_

Kihyun’s smile is too sweet, his eyes too bright. Changkyun’s heartbeat picks up. Her lips slide back around the toothbrush. But the little show of obedience isn’t enough to dodge the impending scolding— she _knows_ it isn’t. She whimpers, her dick quivers, her thoughts go staticky; solemn salutes to her future, thoroughly scolded self.

Kihyun flattens a hand over the nape of her neck and tugs her head down. He twists the toothbrush around to prick at her tongue’s squishy underside with the bristles. Changkyun jerks with every sudden, tiny nip of the bristles, but Kihyun’s face is unmoved, irritated.

“Are you sorry for acting like a brat?”

He forces Changkyun’s mouth open by _pushing_ his fingers into her cheeks, pulls the toothbrush out, and sets it on the sink. Changkyun’s breath swims in wet panic. If she apologizes, Kihyun will finish brushing her teeth. If Kihyun finishes brushing her teeth, he’ll let her get off. If she gets off, she can, _finally,_ go to bed.

So, Changkyun shakes her head.

Kihyun sighs. His eyes slide up to the ceiling, as if to ask the gods what he did to deserve such a stubborn bastard of a baby boy. But, Changkyun isn’t sorry— _especially_ not now that Kihyun forces her ass to hover over his lap and _slaps_ her. Hard.

Changkyun squawks, whiteish spit dribbling out from her mouth.

Kihyun tugs her shorts down, rough and hurried, letting Changkyun gaze miserably at her abandoned dick for a moment, before hitting her again. His wide palm kneads the stinging, bare skin. Changkyun does nothing to stop more drool from creeping down her lip and chin, and onto Kihyun’s shirt.

_“Apologize.”_

“No.” The whisper filters through blankets of bubbles and need, but Kihyun grits his teeth and snarls like he’s reacting to a wailing banshee. He smacks Changkyun’s ass again, and Changkyun feels the sting all the way up to her neck. 

“Disobedient.”

Another smack, and Changkyun’s head fills with melted sugar and popping sparklers.

“Helpless.”

Yet another, and Changkyun nearly chokes on the gobs of foam and spit and that horrible fucking spearmint that _spills_ out of her mouth.

_“Brat."_

Kihyun grips her ass hard, _harder_ , deft fingers clenching —what Changkyun assumes must be— bright red flesh. He raises his eyebrows again. Licks his bottom lip again. And Changkyun can’t do much besides shiver, gape, drool. Her brain isn’t quite— she’s—

“I’m sorry. I-I was bratty. You—” She gulps down Kihyun’s softening gaze. “ _You_ know what’s best. You take care of me. I _want_ you to take care of me.”

Her thighs shake a little from all the hovering and jumping. Her breath comes out in panicked puffs. Her damp eyelashes cling to her cheeks.

Kihyun spares her.

“That’s right. Kihyun knows best.” He smiles. Gently guides her to sit back down. Traces light circles over the small of her back. “Grab our dicks. Jerk us both off. Think you can do that, silly baby?”

Changkyun’s answering nod is stuttered, eager. She’s drowning in the fizzy need to please, to impress, to come. She presses her forehead to Kihyun’s as she gently pulls Kihyun’s dick out of his ugly fleece pajama pants, as she chokes down comments about said ugly fleece pajama pants. Kihyun’s chest swells and shudders.

Changkyun’s hand strokes them both at the careful, even pace Kihyun likes. Glossy, pink skin sliding beneath a calloused palm. Stiff heads knocking against each other. Their stomachs flutter in harmony.

“Kiss me?” Changkyun whispers. Almost reverent. Almost shy.

So, Kihyun kisses her. 

Dry lips smushing into sticky mint. Sharp teeth catching puffy lips. Changkyun’s hand speeds up a bit — _just_ a bit— and Kihyun smiles against her mouth. Nervous heat strangles Changkyun’s core.

Kihyun’s tongue stretches into her mouth. Solid and wet and warm. The tip of it tickles her tongue, and explores her clean, sudsy teeth. Changkyun whines at the light touches, at just having Kihyun in her mouth again.

Kihyun responds by flattening his tongue against her palette, applying pressure up, up into the roof of her mouth. He glides over the little ridges, almost massaging into them. He creeps to the back of Changkyun’s throat and retreats to her front teeth, again and again and _again._

And Changkyun wants to fucking _cry._ There’s something about the wet pressure and the heated exploration. Something about having Kihyun fill her head so strangely, so _completely._ His lips are nearly still, spread widely over Changkyun’s open mouth to make room for his tongue. Wriggling. Tasting. Spit slides between their chins.

Tears fall down Changkyun’s cheeks. It’s hard— _impossible_ to keep up an even pace over their dicks, but she tries. She really, _really_ tries. For Kihyun. Because she’s good— very, _very_ good. Really.

Kihyun's tongue slips over the insides of her teeth. It pushes into the underside of her tongue. It strokes her palette. Changkyun feels fuzzy and wet and ticklish all over, from her very full mouth down to her curling toes. She rises a little with every upward press. She squirms with every curl over her teeth. She cries out.

Changkyun’s grip is reduced to sudden squeezes and loose strokes. Kihyun makes a low, guttural sound as his tongue jabs towards Changkyun’s uvula. Filling her. Stuffing her. _Scaring_ her.

Changkyun jerks and sobs when she comes, Kihyun holding her hips to keep her from falling off of his lap. She blinks at the tile, the toothbrush on the sink, and Kihyun through thin tears.

Kihyun’s face has gone wrinkly. His voice is getting higher, higher. Changkyun grabs his dick with a shaky hand, _begs_ him to come. 

“ _Fuck_ , Kihyun. You’re so perfect and so good. You treat me best, _you_ do.” 

Changkyun twists her wrist, clenches her fingers. Urgent. Desperate.

 _“Please,_ come. You’re— the _best,_ most prettiest, most smartest, _most_ bestest—”

Kihyun’s laugh evaporates into a moan. He grips Changkyun’s ass tight, _tighter_ until his blunt fingernails make Changkyun yelp.

“Kihyun, I need you to come,” Changkyun whines and tilts her head back, returning to face Kihyun with an excess of minty suds and thick spit flowing from her lips, over her chin, down her throat, onto her damp shirtfront. “I need _you._ ”

Kihyun shudders out a curse. Spills over Changkyun’s hands. Connects their foreheads as Changkyun pulls him through the orgasm.

“Better than the nickel?” Kihyun’s hoarse words puff over Changkyun’s face, suffocated by the ungodly amounts of mint in Changkyun’s breath.

“Eh. Debatable.”

“Little shit,” Kihyun laughs and pushes Changkyun from his lap, unceremoniously dumping her on the tile, still leaking sudsy spit. He smiles at Changkyun’s surprise, and begins to leave for their bedroom, when he’s stopped by a whine.

 _“Wait._ I need you.”

Kihyun hovers in the doorway with a skeptical huff.

“I forgot to floss, too.”

**Author's Note:**

> the national dentists' association also recommends kudos n comments to make changkyun's toofs sparkle <33 
> 
> im on [teeth stan twitter](https://twitter.com/showmeurteef) or [cc](https://curiouscat.me/showmeurteef)


End file.
